The present invention is generally directed to photoplethysmographic measurement instruments, and more specifically to disposable pulse oximetry sensors.
A common technique used to monitor blood oxygen levels is pulse oximetry. In this regard, it is known that the light transmissivity and color of blood is a function of the oxygen saturation of the heme in the blood""s hemoglobin. For example, heme that is saturated with oxygen appears bright red because saturated heme is relatively permeable to red light. In contrast, heme that is deoxygenated appears dark and bluish as it is less permeable to red light. A pulse oximeter system measures the oxygen content of arterial blood by utilizing a pulse oximetry sensor to first illuminate the blood with, for example, red and infrared radiation and determine the corresponding amounts of red and infrared radiation that are absorbed by the heme in the blood. In turn, such light absorption amounts may be employed by a pulse oximetry monitor in conjunction with known calibration information to determine blood oxygen levels.
Pulse oximetry sensors generally include one or more light emitters, a detector(s), and a means for holding these components relative to a patient""s tissue. These sensors may generally be classified as reusable or disposable. Reusable sensors typically are more intricate and designed for multiple uses on multiple patients. In this regard, reusable sensors generally must be cleaned between use on different patients. Disposable sensors are typically simplified sensors that are used for a predetermined period on a single patient and discarded. Accordingly, disposable sensors may in some instances be more desirable than their reusable counterparts.
Accordingly, one object of the present invention is to provide a disposable pulse oximetry sensor that has a reduced part count and it therefore easily produced.
Another objective of the present invention is to provide a pulse oximetry sensor that lends itself to production through an automated process.
A further objective of the present invention is to provide a disposable sensor that is economical to manufacture and use while providing required sensor performance.
The inventors of the present invention have recognized the increased need for the use of disposable medical sensors and in particular disposable pulse oximetry sensors. This increased need arises due to, inter alia, concerns in properly cleaning medical instruments between uses of communicable diseases, such as AIDS and Hepatitis B. In this regard, patients as well as hospitals may prefer using new medical instruments, that is, medical instruments that have not been used previously. Additionally, the inventors have recognized that although reusable pulse oximetry sensors tend to initially be more expensive, their ability to be reused may lower their per-use cost below that of disposable pulse oximetry sensors currently existing, leaving hospitals and patients torn between their preferences and the financial realities of the health care system. Accordingly, the inventors have devised a reduced part count pulse oximetry sensor that is easily produced resulting in a disposable pulse oximetry sensor that is cost effective on a per-use basis in comparison with reusable pulse oximetry sensors.
One or more of the above objectives and additional advantages are indeed realized by the present invention where, in one aspect, a pulse oximetry sensor having an integrally formed connector is provided. The sensor includes a substantially clear flexible substrate that may be conformed about a portion of a patient""s tissue, such as a finger. This flexible clear substrate may be formed from any material that provides the desired flexibility and is substantially transparent, allowing for emitting and detecting light signals through this clear substrate. A particularly apt substrate may be made from a polymer thick film (PTF) such as polyester. Mounted on a top surface of the clear flexible substrate is at least one active pulse oximetry component. That is, at least one light emitter, such as a light emitting diode, and/or a light detector, such as a photodiode. Particularly, these active components are mounted on the top surface of the clear substrate such that they emit/detect light through the clear substrate and its bottom surface. In this regard, the clear substrate acts as a lens covering the active surfaces of the light emitter and/or light detector and reducing the overall part count required for the pulse oximetry sensor. Further, as noted, the sensor has an integrally formed connector that allows the flexible substrate to be interconnected to, for example, an electrical pin connector connected to a pulse oximetry monitor.
Various refinements exist of the features noted in relation to the subject first aspect of the present invention. Further features may also be incorporated into the subject first aspect of the present invention as well. These refinements and additional features may exist individually or in any combination. For example, the bottom surface of the clear flexible substrate (i.e., the patient side of the sensor) may contain an adhesive and/or a release liner covering the adhesive for selectively securing the sensor to a patient""s tissue. Additionally, a compressible material layer may be disposed on the patient side surface of the flexible sensor for increased patient comfort. Preferably, any compressible material layer utilized will contain apertures aligned with each light emitter and/or light detector mounted on the top side of the clear flexible substrate, allowing light to be emitted and/or detected through these apertures free from interference. Further, the flexible sensor may contain a light blocking layer applied to the top surface of the clear flexible substrate to minimize the effect of ambient light sources upon the sensor. This light blocking layer may include a separate substrate interconnected to the clear flexible substrate or some sort of opaque coating applied to the top surface of the clear flexible substrate.
Regardless of which additional features the sensor utilizes, in a one embodiment, all materials applied to the bottom surface (i.e., patient side) of the clear flexible substrate contain a substantially clear portion aligned with the active pulse oximetry components. As will be appreciated, this provides for increased light transfer between a light emitter and/or detector upon application to an appendage as well as allowing for the utilization of light (e.g., ultra violet (UV) light or high intensity visible light) to cure various light-curable adhesives that may be used to mount one or more of the components to the clear flexible substrate during manufacture. For example, the light emitter and/or detector may be encapsulated on top of the clear substrate using a light-curable clear adhesive to stabilize the emitter/detector as well as provide increased focusing of light into or from the clear substrate. Light may be applied through these layers and the bottom surface of the clear substrate to cure the adhesive(s). In a further embodiment, all the materials applied to the bottom surface of the clear substrate will be at least partially transparent materials to allow light curable adhesives to be utilized in laminating the various materials together. In addition, or alternatively, thermal and/or mechanical pressure may be utilized to initiate or complete the cure of adhesives as well as thermally bond (i.e., laminate) one or more of the various material layers together.
In a second aspect of the present invention, a pulse oximetry sensor is provided comprising a substantially clear flexible substrate that may be conformed about a patient""s tissue having, mounted on its top surface, at least one active pulse oximetry component. Again these active components (i.e., light emitter and/or light detector) are mounted on the clear substrate""s top surface such that they emit/detect light through the clear substrate and its bottom surface. Further, the sensor includes at least one electrically conductive trace formed on the clear flexible substrate. The electrically conductive trace(s) is formed on the same surface (i.e., top surface) on which the emitters/detectors are mounted and provides an electrical connection between the integrally formed connector and the active components. This trace may be formed of any appropriate conductive material so long as it allows the substrate to freely flex. Examples of appropriate materials include thin metallic foils (e.g., 0.001 in) that may be stamped onto and/or melted into the clear substrate and conductive inks that may be printed onto the clear substrate.
Light emitters and detectors typically include a semiconductor die that contains first and second electrical contact pads that must be electrically interconnected with a power source to function. In this regard the light emitter and/or detector will be electrically interconnected to at least one electronically conductive trace. That is the emitter/detector may be mounted such that it electrically contacts the conductive trace using, for example, a conductive epoxy to attach an electrical contact pad on the emitter/detector to one or more electrically conductive traces.
Various refinements exist of the features in relation to the subject second aspect of the present invention. For example, the clear flexible substrate may have a plurality of electrical conductive traces formed on the surface containing the emitter and/or detector. In this regard, the active components (i.e., emitter and detector) may each be electrically interconnected to first and second electrical traces. That is, each active component may be electrically interconnected to xe2x80x9coutxe2x80x9d and xe2x80x9creturnxe2x80x9d legs of what forms an electrical circuit when the sensor is connected to a pulse oximetry monitor. Further, the subject second aspect of the present invention may utilize any additional components interconnected to the flexible substrate such as those discussed above in reference to the first aspect of the present invention. Again, any additional components interconnected to the bottom surface of the subject second aspect of the present invention will preferably be at least partially transparent to realize the above described benefits.
In one embodiment of the second aspect of the present invention, the conductive traces are formed on the clear flexible substrate using a conductive ink, such as a silver epoxy, that is deposited onto the clear substrate. In this regard, the conductive traces may be deposited on the clear flexible substrate using a printing process such as, but not limited to, inkjet printing, screen printing, or pad printing. As will be appreciated, the use of ink printing allows for formation of conductive traces on the clear flexible substrate in a simplified manner in comparison to the utilization of, for example, chemical etching of a conductive surface such as copper, the use of a stamped lead frame, and/or the use of discrete wire conductors.
In a related aspect of the present invention, a pulse oximetry sensor is provided having a clear flexible substrate with at least one electrically conductive trace formed thereon and at least one light emitter electrically interconnected to one or more of those traces. The sensor further includes a thermal element adapted to transfer thermal energy away from the light emitter. As will be appreciated, when the light emitter is active (i.e., emitting light) the light emitter and the clear substrate to which it is mounted may become uncomfortably warm. This is especially evident where conductive ink traces are utilized on the clear flexible substrate, as conductive ink traces may not have enough thermal mass to effectively transfer heat away from the light emitter. Accordingly, undue heat build up around the light emitter may result in patient discomfort and/or tissue damage. Though in the present invention the thermal element is utilized to counteract the reduced thermal mass resulting from use of printed conductive traces, it will be appreciated that a thermal element may also be utilized with any pulse oximetry sensor to reduce potentially damaging heat concentrations. The thermal element may be formed of any material having high thermal conductivity such as, but not limited to, a copper sheet or washer that is thermally connected to the light emitter. In any case, the thermal element acts as a heat sink operable to draw heat away from the light emitter and dissipate that heat over an increased area to prevent excessive heat build up in a single area adjacent to a patient""s tissue.
A related aspect of the present invention provides a sensor utilizing a clear flexible substrate on which a light emitter and/or detector is mounted for emitting/detecting light through the clear flexible substrate. This sensor further incorporates an insulative layer in a face-to-face relationship with at least a portion of a patient side surface (i.e., the bottom surface of the clear substrate) for creating a temperature differential between a patient""s tissue and the bottom surface of the clear flexible substrate. As noted above, sensor active components and, in particular, the light emitting components may become uncomfortably warm during normal usage. In this regard, the insulative layer may be disposed on the bottom surface of the clear flexible substrate to provide a thermal buffer or xe2x80x9cstand-offxe2x80x9d between a patient""s tissue and the bottom surface of the clear substrate.
In one embodiment, this insulative layer will contain apertures aligned with each of the active components mounted on the top surface of the clear flexible substrate. This arrangement allows the active components to emit/detect light free from interference. In a further embodiment utilizing the insulative layer, a substantially clear interconnecting layer will be interconnected to patient side surface of the insulative layer allowing the apertures within the insulative layer to be sandwiched between the clear interconnecting layer and the patient surface of the clear substrate. As will be appreciated, this produces an air pocket of xe2x80x9cdeadxe2x80x9d air space between the patient""s tissue and the bottom surface of the clear substrate, further reducing the possibility of undue heat build up against a patient""s tissue. This pocket is preferably sealed to prevent the pocket deflation when the sensor is applied to the patient""s tissue. Adhesives and/or thermal bonding of the various layers may be utilized to producing a sealed pocket.
In a further related aspect of the present invention, the flexible pulse oximetry sensor utilizes a first substrate having a top surface with one or more electrically conductive traces formed thereon and a second flexible substrate having a bottom surface with one or more electrical conductive traces formed thereon. In this embodiment, one or more active sensor components (i.e. light emitters/detectors) are physically and electronically mounted to one of the substrates as well as being electrically interconnected to a conductive trace on the second flexible substrate. In this regard, the first and second flexible substrates may be disposed in a face-to-face relationship where the top and bottom surfaces containing the electrically conductive traces are disposed towards one another. As will be appreciated, this provides a sensor where the electrical traces, such as printed conductive ink traces, as well as the active sensor components are sandwiched between the first and second substrates and are thereby protected from the environment.
One or more of the above noted objectives and advantages may also be realized by an inventive method for forming a pulse oximetry sensor. The inventive method includes the steps of mounting onto the top surface of a substantially clear substrate, a light emitter for emitting light through the bottom surface of the substrate and/or a light detector for detecting light through the bottom surface of the substrate. The step of mounting may further include the step of electrically connecting the emitter/detector to one or more electrical traces associated with the clear substrate using, for example, a conductive epoxy. The mounting step may also include encapsulating the emitter/detector with a clear adhesive for increasing the light focusing capabilities of that component. The method further includes the step of applying light through the bottom surface of the clear substrate to at least partially cure one or more light-curable adhesives used for mounting emitters/detectors to the clear substrate.
A method is also provided for producing a flexible sensor having an integrally formed cord as well as an integrally formed connector. The process includes the steps of depositing at least one electrically conductive trace between first and second points on the surface of a flexible substrate sheet, which may be a clear flexible substrate. In order to produce an integrally formed cord having a length greater than that of the longest edge of the flexible substrate sheet, these traces are formed in a concentric pattern, continuously winding about a first point and gradually approaching a second point. For example, a first point may be located near the middle of a substantially square substrate sheet while the second point is located at one of the corners of the substrate sheet. The electrical traces connect the first and second points by winding about the first point in, for example, a circular or rectangular spiral pattern until they reach the second point. In one embodiment, the electrically conductive traces are formed between the first and second points on the substrate sheet using a conductive ink printing processes. Additionally, at least one light emitter and/or light detector are mounted on the flexible substrate and are electrically interconnected the conductive traces. Preferably, these emitters/detectors are mounted at the end of a trace to maximize the resulting length of the cord. Finally, the flexible substrate is cut between concentric windings of the electrical trace between the first and second points to form a flexible concentric strip having at least one electrically conductive trace between its first and second ends. This flexible concentric strip is then straightened to provide a flexible sensor having an integrally formed cord.